Amsterdam (CNN)Each month, thousands of tourists come to De Wallen, Amsterdam's red light district. In between a network of narrow alleyways, interconnected bridges and canals they wander past the coffee shops and the infamous sex workers behind the windows.

It's here that Toos Heemskerk-Schep began her career as a social worker and first came into contact with human trafficking.

Today she is the head of Not For Sale in The Netherlands, a branch of an American NGO dedicated to providing long-term opportunities for survivors of modern slavery and exploitation.

Not all of those who work in De Wallen are there against their will. Since prostitution was legalized in 2000 the city has balanced maintaining the spirit of liberalism that allows for sex to be sold openly, providing a legal framework for the sex workers to operate, and curbing criminality.

Now, gentrification is taking effect. Amsterdam's property market has become a magnet for investment. The social landscape is changing. Red light windows are closing. But on a walk through the red light area Heemskerk-Schep explains what she encountered before the full legalization of prostitution.

"When I started in 1995 ... we had tolerated prostitution in this area," she says. "At that time it was just incredible what was going on."

She points to a street near to the Old Church. "That area there was full of Nigerian girls, girls who came from Edo State, who started off with a debt of $40,000 that they had to pay back to their traffickers.

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"It was just after the opening of the Iron Curtain and so we got all of a sudden a whole group of eastern European girls into the Netherlands. It was really just by having my feet in this area and talking and having conversations with the girls ... that I started to learn about their situations."

She gestures to another street close by: "The street behind me was a street where only Hungarian girls were working. Now and then the girls approached me, sharing that they were trafficked or exploited.

"When they had to be taken out by the police and taken to a safe house, then I learnt that, OK, now they are in the safe house, now what? How are they going build up their future again? How do they get skills in order to re-integrate into society?"

'Do good, eat well'

Heemskerk-Schep was frustrated and wanted to do more than her social work allowed. This led to her collaboration with the Not For Sale Foundation. An idea formed to build a profitable eatery where trafficked survivors would train, gain qualifications and work alongside professionals.

After four years of planning, restaurant Dignita opened in 2015. Its motto: Do Good, Eat Well.

The restaurant has already built a loyal customer base in the area. It supplements donations with income generated from the restaurant. To date, some 162 trainees have joined the program.

Graduates leave with more than a certificate. The day-to-day normal social interaction in a safe environment helps survivors overcome their past trauma, says Heemskerk-Schep.

"Only focusing on job training is not enough," she says. "It's incredibly important also that they become part of our community here."

The nature of how she came to The Netherlands is difficult for her to explain fully. Exploited as a domestic worker, it is still hard for her to speak about it before tears start to flow. Dignita, she says, saved her life.

"When I moved to the government shelter it was difficult," she says. "I always wanted to kill myself. There was no energy in my body.

"Whilst there I was asked about whether I wanted to go for training. I didn't know what Not for Sale meant ... but afterwards I gave it some thought and I said: you know what? I will just have a look for a day to see what it is.

"I was happy there, and afterwards I went again. I am always happy when I cook.

"I felt like a flower without water. But when I started the training, I got my energy back."

For Hanan, training has proved inspirational, and she now dreams of becoming a chef.

'We want to be their voice'

One of the first dishes trainees learn to cook is soup. Twice a week it's biked from the restaurant to the Dignita store and information center in the red light district. From here, volunteers deliver takeout orders to the sex workers behind the windows.

"The soup outreach and whatever we are doing here is just an opportunity to be in contact with them ... and to reach out to them but also to learn from them," says Heemskerk-Schep.

"The fact is that at the moment I have three girls coming from the windows who have been exploited, who have been forced to work as a prostitute. And although we have a legalized system, it doesn't mean to say that the crime is totally out of this business.

"There are still girls who have been exploited ... and for those we want to be there and be their voice."

Heemskerk-Schep has ambitions to scale Dignita's self-sustaining business model beyond Amsterdam, and help more women like Hanan.

"If someone reaches out a hand to you and says 'join me, stand up,' you should join," says Hanan.

"Not For Sale gave me the hand and I trusted them [enough] to follow. I didn't have energy but I did go. I am no longer in bed. Stand up. It is really good."